Dynamic Ground Effect on the Longitudinal Stability of Airplanes during the Landing

The objective of the work presented herein is to study the influence of dynamic ground effect on the longitudinal stability of airplanes during un-power landing by numerical simulation. A method was developed to design a landing control system which considers dynamic ground effect by the inclusion of the h derivatives in the longitudinal equations of motion. A case study was presented to illustrate with an example the influence of dynamic ground effect on the longitudinal stability using the Unmanned Airplane for Ecological Conservation. Open-loop flight simulations were performed considering dynamic ground effect using a program written in FORTRAN language. When the vehicle achieved heights lower than 2.5935 m during the simulations, an unstable response appears. A landing control system was designed using the methodology presented in this paper, and close-loop simulations were completed using a model created in Simulink. The control system drove the airplane to the runway, only when the h derivatives were included in the equations of motion. The unstable response produced by the dynamic ground effect has a strong influence in the flare manoeuvre, and for this reason, in the design of a landing control system, the h derivatives must be included in the longitudinal equations of motion.